Charged particle beam systems can be used to inspect specimens such as wafers during semiconductor processing. Detectors can be used to image the specimens or to determine a composition of the specimens. For example, an electron detector may be used to image a specimen by detecting secondary electrons emitted from the specimen and/or backscattered electrons reflected from the specimen. As another example, an energy dispersion x-ray detector (EDX) can be used for determining a composition of a specimen. An EDX detector collects x-ray photons emitted from the specimen and generates an energy spectrum. Energy spectrum means any type of information about energy levels at different wavelengths or frequencies along the spectrum. For example—the energy spectrum can be a histogram that displays the number of X-ray counts for each x-ray energy level. Measuring x-ray energies can help to characterize the element from which an x-ray photon was emitted.
The column that illuminates the specimen is proximate to the specimen and has a relatively big tip. The tip may prevent the detector from being positioned in proximity of the specimen, and often the detector is positioned in an asymmetrical manner in relation to an axis of illumination thereby providing a partial and asymmetrical angular coverage of x-ray photons and/or charged particles emitted or reflected from the specimen.
There is a growing need to improve the accuracy of charge particle beam measurements.